1. Field of the Invention
The present invention relates to an intelligent security system including a truly passive transceiver means which may be attached to virtually any object so that the intelligent security system may be utilized to identify and process information concerning the particular object to which the passive transceiver is attached. Power to operate the passive transceiver is derived from electromagnetic radiation, preferably in the form of encrypted radio frequency energy, which is transmitted by a scanner which is one element of the security system. The passive transceiver includes circuitry capable of both rectifying and decoding the encrypted radio frequency power. If a predetermined radio frequency message is received by the passive transceiver, its transmit circuitry will then be energized to provide an encoded response. The encoded response is received by the scanner means and provided to a decoder, and that decoded response is then fed to a central processing unit for operation of the security system in accord with pre-programmed instructions.
Throughout the specification and claims of this patent, it is to be understood that the term "passive" is meant to indicate operability without connection to an external power source and also without the necessity for any internal power source such as a battery.
2. Description of the Prior Art
The prior art discloses and teaches numerous devices which are useful for providing locator information and/or access to controlled spaces by the use of a passive card or tag. For example, virtually all automatic teller machines require the insertion of a magnetically-encoded card for proper operation of that machine. Similar, magnetically-encoded devices are frequently used as key cards to provide access to controlled spaces or as fee cards for toll booths or vending machines. However, utilization of such magnetically-encoded cards invariably requires that the card be properly inserted into the device to be actuated so that the code embedded therein may be read.
Prior patent literature teaches another form of passive security tags which are energized by electromagnetic radiation from a remote source. One such device is disclosed in U.S. Pat. No. 4,857,893 to Carroll. According to the disclosure of that patent, a transponder device receives a carrier signal from an interrogator unit. Circuitry within the transponder device rectifies the carrier signal to generate operating power, and logic circuits within the transponder device then respond by broadcasting a reply data word which is received and processed by the interrogator unit which provided the initial carrier signal. The disclosure of this Carroll patent is particularly pertinent, for the transponder device is constructed by providing all electrical circuits on a single monolithic semiconductor chip. However, it must be noted that the output from the Carroll transponder device is a submultiple of the input, or carrier, frequency, and there is no real security with regard to that incoming frequency. A predetermined frequency will trigger any corresponding transponder device by which it is received.
U.S. Pat. No. 4,688,026 to Scribner, et al., discloses a method for collecting and using data associated with tagged objects wherein radio frequency energy is used to activate tags capable of wirelessly transmitting unique codes. However, according to the disclosure of this Scribner patent, there is no encryption of the interrogating signal so that any tag capable of receiving the broadcast interrogation frequency will be activated to respond.
Yet another device utilizing what are referred to as "passive transceivers" for the purpose of monitoring location, identification, movement, or inventory of items is disclosed in U.S. Pat. No. 4,656,463 to Anders, et al. However, notwithstanding that patent's use of the word "passive," the disclosure of this patent is quite clear that its "passive transceiver" is actually battery-powered.
Still another identification system, which does utilize a passive transponder, is taught in U.S. Pat. No. 4,730,188, to Milheiser. As with other similar prior art devices, the Milheiser system includes a passive integrated transponder attached to or embedded in an item to be identified which is actuated by an inductive coupling from an interrogator. Upon actuation, the passive integrated transponder responds to the integrator via the inductive coupling with a signal consisting of a stream of data unique to that particular item. However, also as with the similar prior art devices, the Milheiser system does not disclose or teach an encrypted interrogation signal which is firs decoded by the passive integrated transponder before its transmit circuit may be actuated to provide data.
U.S. Pat. No. 4,260,983 to Falck, et al., discloses a presence sensing detector and a system for detecting an article by virtue of a receiver/transmitter affixed to that article. However, according to the disclosure of this patent, the detector is always transmitting its interrogation signal, and as with the other devices identified above, there is not security code, or encryption, associated with the incoming signal.
Two prior art inventory data acquisition systems are represented by U.S. Pat. No. 4,673,932 and U.S. Pat. No. 4,862,160, both to Ekchian, et al. According to the disclosures of those patents, a computerized transceiver repeatedly sweeps through a set of transmit/receive frequencies to interrogate collectively a plurality of items. Items in each group are tagged with a printed circuit transponder tuned to frequencies uniquely assigned to each group. The printed circuit transponders reply to the computerized transceiver for accumulation of inventory control data. However, the replies are frequency coded only, no digital data is transmitted, and, as above, the interrogating signal could only be said to be frequency coded, and not encrypted.
Two other prior art patents have been noted and are deemed pertinent to the general scope of the present invention. U. S. Pat. No. 4,475,481 to Carroll relates to an identification system comprising an intermittent electromagnetic generator at one frequency and a remote receiver for receiving the electromagnetic energy and using it to power an encoder of digital information. Clearly, there is no real security associated with this identification system, for the remote receiver will respond to any incoming signal so long as it is simply of a predetermined frequency. U.S. Pat. No. 4,931,788 to Creswick discloses a transponder for receiving a modulated interrogating signal, means for demodulating the received signal to produce a periodic base band signal, and means for transmitting data at a rate determined by periodicity of that base band signal. As with the other prior art devices noted, there is no incoming security code which must be decoded before the transponder of this invention will respond with its data information.
It is therefore quite clear that there remains a significant need in the art for an intelligent security system utilizing a truly passive transceiver capable of receiving and decoding a incoming interrogation signal before being actuated to generate and transmit unique data information held by the passive transceiver.